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django/docs/ref/request-response.txt
Malcolm Tredinnick 04ff1aff12 Fixed #9712 -- Documented how HTTP headers are converted to request.META keys. 
Based on a patch from masklinn.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@9579 bcc190cf-cafb-0310-a4f2-bffc1f526a37
2008-12-07 03:41:54 +00:00

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.. _ref-request-response:
============================
Request and response objects
============================
.. module:: django.http
:synopsis: Classes dealing with HTTP requests and responses.
Quick overview
==============
Django uses request and response objects to pass state through the system.
When a page is requested, Django creates an :class:`HttpRequest` object that
contains metadata about the request. Then Django loads the appropriate view,
passing the :class:`HttpRequest` as the first argument to the view function. Each
view is responsible for returning an :class:`HttpResponse` object.
This document explains the APIs for :class:`HttpRequest` and :class:`HttpResponse`
objects.
HttpRequest objects
===================
.. class:: HttpRequest
Attributes
----------
All attributes except ``session`` should be considered read-only.
.. attribute:: HttpRequest.path
A string representing the full path to the requested page, not including
the domain.
Example: ``"/music/bands/the_beatles/"``
.. attribute:: HttpRequest.method
A string representing the HTTP method used in the request. This is
guaranteed to be uppercase. Example::
if request.method == 'GET':
do_something()
elif request.method == 'POST':
do_something_else()
.. attribute:: HttpRequest.encoding
.. versionadded:: 1.0
A string representing the current encoding used to decode form submission
data (or ``None``, which means the ``DEFAULT_CHARSET`` setting is used).
You can write to this attribute to change the encoding used when accessing
the form data. Any subsequent attribute accesses (such as reading from
``GET`` or ``POST``) will use the new ``encoding`` value. Useful if you
know the form data is not in the ``DEFAULT_CHARSET`` encoding.
.. attribute:: HttpRequest.GET
A dictionary-like object containing all given HTTP GET parameters. See the
``QueryDict`` documentation below.
.. attribute:: HttpRequest.POST
A dictionary-like object containing all given HTTP POST parameters. See the
``QueryDict`` documentation below.
It's possible that a request can come in via POST with an empty ``POST``
dictionary -- if, say, a form is requested via the POST HTTP method but
does not include form data. Therefore, you shouldn't use ``if request.POST``
to check for use of the POST method; instead, use ``if request.method ==
"POST"`` (see above).
Note: ``POST`` does *not* include file-upload information. See ``FILES``.
.. attribute:: HttpRequest.REQUEST
For convenience, a dictionary-like object that searches ``POST`` first,
then ``GET``. Inspired by PHP's ``$_REQUEST``.
For example, if ``GET = {"name": "john"}`` and ``POST = {"age": '34'}``,
``REQUEST["name"]`` would be ``"john"``, and ``REQUEST["age"]`` would be
``"34"``.
It's strongly suggested that you use ``GET`` and ``POST`` instead of
``REQUEST``, because the former are more explicit.
.. attribute:: HttpRequest.COOKIES
A standard Python dictionary containing all cookies. Keys and values are
strings.
.. attribute:: HttpRequest.FILES
A dictionary-like object containing all uploaded files. Each key in
``FILES`` is the ``name`` from the ``<input type="file" name="" />``. Each
value in ``FILES`` is an ``UploadedFile`` object containing the following
attributes:
* ``read(num_bytes=None)`` -- Read a number of bytes from the file.
* ``name`` -- The name of the uploaded file.
* ``size`` -- The size, in bytes, of the uploaded file.
* ``chunks(chunk_size=None)`` -- A generator that yields sequential chunks of data.
See :ref:`topics-files` for more information.
Note that ``FILES`` will only contain data if the request method was POST
and the ``<form>`` that posted to the request had
``enctype="multipart/form-data"``. Otherwise, ``FILES`` will be a blank
dictionary-like object.
.. versionchanged:: 1.0
In previous versions of Django, ``request.FILES`` contained simple ``dict``
objects representing uploaded files. This is no longer true -- files are
represented by ``UploadedFile`` objects as described below.
These ``UploadedFile`` objects will emulate the old-style ``dict``
interface, but this is deprecated and will be removed in the next release of
Django.
.. attribute:: HttpRequest.META
A standard Python dictionary containing all available HTTP headers.
Available headers depend on the client and server, but here are some
examples:
* ``CONTENT_LENGTH``
* ``CONTENT_TYPE``
* ``HTTP_ACCEPT_ENCODING``
* ``HTTP_ACCEPT_LANGUAGE``
* ``HTTP_HOST`` -- The HTTP Host header sent by the client.
* ``HTTP_REFERER`` -- The referring page, if any.
* ``HTTP_USER_AGENT`` -- The client's user-agent string.
* ``QUERY_STRING`` -- The query string, as a single (unparsed) string.
* ``REMOTE_ADDR`` -- The IP address of the client.
* ``REMOTE_HOST`` -- The hostname of the client.
* ``REQUEST_METHOD`` -- A string such as ``"GET"`` or ``"POST"``.
* ``SERVER_NAME`` -- The hostname of the server.
* ``SERVER_PORT`` -- The port of the server.
With the exception of ``CONTENT_LENGTH`` and ``CONTENT_TYPE``, as given
above, any HTTP headers in the request are converted to ``META`` keys by
converting all characters to uppercase, replacing any hyphens with
underscores and adding an ``HTTP_`` prefix to the name. So, for example, a
header called ``X-Bender`` would be mapped to the ``META`` key
``HTTP_X_BENDER``.
.. attribute:: HttpRequest.user
A ``django.contrib.auth.models.User`` object representing the currently
logged-in user. If the user isn't currently logged in, ``user`` will be set
to an instance of ``django.contrib.auth.models.AnonymousUser``. You
can tell them apart with ``is_authenticated()``, like so::
if request.user.is_authenticated():
# Do something for logged-in users.
else:
# Do something for anonymous users.
``user`` is only available if your Django installation has the
``AuthenticationMiddleware`` activated. For more, see
:ref:`topics-auth`.
.. attribute:: HttpRequest.session
A readable-and-writable, dictionary-like object that represents the current
session. This is only available if your Django installation has session
support activated. See the :ref:`session documentation
<topics-http-sessions>` for full details.
.. attribute:: HttpRequest.raw_post_data
The raw HTTP POST data. This is only useful for advanced processing. Use
``POST`` instead.
.. attribute:: HttpRequest.urlconf
Not defined by Django itself, but will be read if other code (e.g., a custom
middleware class) sets it. When present, this will be used as the root
URLconf for the current request, overriding the ``ROOT_URLCONF`` setting.
See :ref:`how-django-processes-a-request` for details.
Methods
-------
.. method:: HttpRequest.get_host()
.. versionadded:: 1.0
Returns the originating host of the request using information from the
``HTTP_X_FORWARDED_HOST`` and ``HTTP_HOST`` headers (in that order). If
they don't provide a value, the method uses a combination of
``SERVER_NAME`` and ``SERVER_PORT`` as detailed in `PEP 333`_.
.. _PEP 333: http://www.python.org/dev/peps/pep-0333/
Example: ``"127.0.0.1:8000"``
.. method:: HttpRequest.get_full_path()
Returns the ``path``, plus an appended query string, if applicable.
Example: ``"/music/bands/the_beatles/?print=true"``
.. method:: HttpRequest.build_absolute_uri(location)
.. versionadded:: 1.0
Returns the absolute URI form of ``location``. If no location is provided,
the location will be set to ``request.get_full_path()``.
If the location is already an absolute URI, it will not be altered.
Otherwise the absolute URI is built using the server variables available in
this request.
Example: ``"http://example.com/music/bands/the_beatles/?print=true"``
.. method:: HttpRequest.is_secure()
Returns ``True`` if the request is secure; that is, if it was made with
HTTPS.
.. method:: HttpRequest.is_ajax()
.. versionadded:: 1.0
Returns ``True`` if the request was made via an ``XMLHttpRequest``, by checking
the ``HTTP_X_REQUESTED_WITH`` header for the string ``'XMLHttpRequest'``. The
following major JavaScript libraries all send this header:
* jQuery
* Dojo
* MochiKit
* MooTools
* Prototype
* YUI
If you write your own XMLHttpRequest call (on the browser side), you'll
have to set this header manually if you want ``is_ajax()`` to work.
QueryDict objects
-----------------
.. class:: QueryDict
In an :class:`HttpRequest` object, the ``GET`` and ``POST`` attributes are instances
of ``django.http.QueryDict``. :class:`QueryDict` is a dictionary-like
class customized to deal with multiple values for the same key. This is
necessary because some HTML form elements, notably
``<select multiple="multiple">``, pass multiple values for the same key.
``QueryDict`` instances are immutable, unless you create a ``copy()`` of them.
That means you can't change attributes of ``request.POST`` and ``request.GET``
directly.
Methods
-------
:class:`QueryDict` implements all the standard dictionary methods, because it's
a subclass of dictionary. Exceptions are outlined here:
.. method:: QueryDict.__getitem__(key)
Returns the value for the given key. If the key has more than one value,
``__getitem__()`` returns the last value. Raises
``django.utils.datastructure.MultiValueDictKeyError`` if the key does not
exist. (This is a subclass of Python's standard ``KeyError``, so you can
stick to catching ``KeyError``.)
.. method:: QueryDict.__setitem__(key, value)
Sets the given key to ``[value]`` (a Python list whose single element is
``value``). Note that this, as other dictionary functions that have side
effects, can only be called on a mutable ``QueryDict`` (one that was created
via ``copy()``).
.. method:: QueryDict.__contains__(key)
Returns ``True`` if the given key is set. This lets you do, e.g., ``if "foo"
in request.GET``.
.. method:: QueryDict.get(key, default)
Uses the same logic as ``__getitem__()`` above, with a hook for returning a
default value if the key doesn't exist.
.. method:: QueryDict.setdefault(key, default)
Just like the standard dictionary ``setdefault()`` method, except it uses
``__setitem__`` internally.
.. method:: QueryDict.update(other_dict)
Takes either a ``QueryDict`` or standard dictionary. Just like the standard
dictionary ``update()`` method, except it *appends* to the current
dictionary items rather than replacing them. For example::
>>> q = QueryDict('a=1')
>>> q = q.copy() # to make it mutable
>>> q.update({'a': '2'})
>>> q.getlist('a')
['1', '2']
>>> q['a'] # returns the last
['2']
.. method:: QueryDict.items()
Just like the standard dictionary ``items()`` method, except this uses the
same last-value logic as ``__getitem()__``. For example::
>>> q = QueryDict('a=1&a=2&a=3')
>>> q.items()
[('a', '3')]
.. method:: QueryDict.values()
Just like the standard dictionary ``values()`` method, except this uses the
same last-value logic as ``__getitem()__``. For example::
>>> q = QueryDict('a=1&a=2&a=3')
>>> q.values()
['3']
In addition, ``QueryDict`` has the following methods:
.. method:: QueryDict.copy()
Returns a copy of the object, using ``copy.deepcopy()`` from the Python
standard library. The copy will be mutable -- that is, you can change its
values.
.. method:: QueryDict.getlist(key)
Returns the data with the requested key, as a Python list. Returns an
empty list if the key doesn't exist. It's guaranteed to return a list of
some sort.
.. method:: QueryDict.setlist(key, list_)
Sets the given key to ``list_`` (unlike ``__setitem__()``).
.. method:: QueryDict.appendlist(key, item)
Appends an item to the internal list associated with key.
.. method:: QueryDict.setlistdefault(key, default_list)
Just like ``setdefault``, except it takes a list of values instead of a
single value.
.. method:: QueryDict.lists()
Like :meth:`items()`, except it includes all values, as a list, for each
member of the dictionary. For example::
>>> q = QueryDict('a=1&a=2&a=3')
>>> q.lists()
[('a', ['1', '2', '3'])]
.. method:: QueryDict.urlencode()
Returns a string of the data in query-string format.
Example: ``"a=2&b=3&b=5"``.
HttpResponse objects
====================
.. class:: HttpResponse
In contrast to :class:`HttpRequest` objects, which are created automatically by
Django, :class:`HttpResponse` objects are your responsibility. Each view you
write is responsible for instantiating, populating and returning an
:class:`HttpResponse`.
The :class:`HttpResponse` class lives in the ``django.http`` module.
Usage
-----
Passing strings
~~~~~~~~~~~~~~~
Typical usage is to pass the contents of the page, as a string, to the
:class:`HttpResponse` constructor::
>>> response = HttpResponse("Here's the text of the Web page.")
>>> response = HttpResponse("Text only, please.", mimetype="text/plain")
But if you want to add content incrementally, you can use ``response`` as a
file-like object::
>>> response = HttpResponse()
>>> response.write("<p>Here's the text of the Web page.</p>")
>>> response.write("<p>Here's another paragraph.</p>")
You can add and delete headers using dictionary syntax::
>>> response = HttpResponse()
>>> response['X-DJANGO'] = "It's the best."
>>> del response['X-PHP']
>>> response['X-DJANGO']
"It's the best."
Note that ``del`` doesn't raise ``KeyError`` if the header doesn't exist.
Passing iterators
~~~~~~~~~~~~~~~~~
Finally, you can pass ``HttpResponse`` an iterator rather than passing it
hard-coded strings. If you use this technique, follow these guidelines:
* The iterator should return strings.
* If an :class:`HttpResponse` has been initialized with an iterator as its
content, you can't use the class:`HttpResponse` instance as a file-like
object. Doing so will raise ``Exception``.
Setting headers
~~~~~~~~~~~~~~~
To set a header in your response, just treat it like a dictionary::
>>> response = HttpResponse()
>>> response['Pragma'] = 'no-cache'
Telling the browser to treat the response as a file attachment
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
To tell the browser to treat the response as a file attachment, use the
``mimetype`` argument and set the ``Content-Disposition`` header. For example,
this is how you might return a Microsoft Excel spreadsheet::
>>> response = HttpResponse(my_data, mimetype='application/vnd.ms-excel')
>>> response['Content-Disposition'] = 'attachment; filename=foo.xls'
There's nothing Django-specific about the ``Content-Disposition`` header, but
it's easy to forget the syntax, so we've included it here.
Attributes
----------
.. attribute:: HttpResponse.content
A normal Python string representing the content, encoded from a Unicode
object if necessary.
Methods
-------
.. method:: HttpResponse.__init__(content='', mimetype=None, status=200, content_type=DEFAULT_CONTENT_TYPE)
Instantiates an ``HttpResponse`` object with the given page content (a
string) and MIME type. The ``DEFAULT_CONTENT_TYPE`` is ``'text/html'``.
``content`` can be an iterator or a string. If it's an iterator, it should
return strings, and those strings will be joined together to form the
content of the response.
``status`` is the `HTTP Status code`_ for the response.
.. versionadded:: 1.0
``content_type`` is an alias for ``mimetype``. Historically, this parameter
was only called ``mimetype``, but since this is actually the value included
in the HTTP ``Content-Type`` header, it can also include the character set
encoding, which makes it more than just a MIME type specification.
If ``mimetype`` is specified (not ``None``), that value is used.
Otherwise, ``content_type`` is used. If neither is given, the
``DEFAULT_CONTENT_TYPE`` setting is used.
.. method:: HttpResponse.__setitem__(header, value)
Sets the given header name to the given value. Both ``header`` and
``value`` should be strings.
.. method:: HttpResponse.__delitem__(header)
Deletes the header with the given name. Fails silently if the header
doesn't exist. Case-sensitive.
.. method:: HttpResponse.__getitem__(header)
Returns the value for the given header name. Case-sensitive.
.. method:: HttpResponse.has_header(header)
Returns ``True`` or ``False`` based on a case-insensitive check for a
header with the given name.
.. method:: HttpResponse.set_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=None)
Sets a cookie. The parameters are the same as in the `cookie Morsel`_
object in the Python standard library.
* ``max_age`` should be a number of seconds, or ``None`` (default) if
the cookie should last only as long as the client's browser session.
* ``expires`` should be a string in the format
``"Wdy, DD-Mon-YY HH:MM:SS GMT"``.
* Use ``domain`` if you want to set a cross-domain cookie. For example,
``domain=".lawrence.com"`` will set a cookie that is readable by
the domains www.lawrence.com, blogs.lawrence.com and
calendars.lawrence.com. Otherwise, a cookie will only be readable by
the domain that set it.
.. _`cookie Morsel`: http://docs.python.org/library/cookie.html#Cookie.Morsel
.. method:: HttpResponse.delete_cookie(key, path='/', domain=None)
Deletes the cookie with the given key. Fails silently if the key doesn't
exist.
Due to the way cookies work, ``path`` and ``domain`` should be the same
values you used in ``set_cookie()`` -- otherwise the cookie may not be
deleted.
.. method:: HttpResponse.write(content)
This method makes an :class:`HttpResponse` instance a file-like object.
.. method:: HttpResponse.flush()
This method makes an :class:`HttpResponse` instance a file-like object.
.. method:: HttpResponse.tell()
This method makes an :class:`HttpResponse` instance a file-like object.
.. _HTTP Status code: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10
.. _ref-httpresponse-subclasses:
HttpResponse subclasses
-----------------------
Django includes a number of ``HttpResponse`` subclasses that handle different
types of HTTP responses. Like ``HttpResponse``, these subclasses live in
:mod:`django.http`.
.. class:: HttpResponseRedirect
The constructor takes a single argument -- the path to redirect to. This
can be a fully qualified URL (e.g. ``'http://www.yahoo.com/search/'``) or an
absolute URL with no domain (e.g. ``'/search/'``). Note that this returns
an HTTP status code 302.
.. class:: HttpResponsePermanentRedirect
Like :class:`HttpResponseRedirect`, but it returns a permanent redirect
(HTTP status code 301) instead of a "found" redirect (status code 302).
.. class:: HttpResponseNotModified
The constructor doesn't take any arguments. Use this to designate that a
page hasn't been modified since the user's last request (status code 304).
.. class:: HttpResponseBadRequest
.. versionadded:: 1.0
Acts just like :class:`HttpResponse` but uses a 400 status code.
.. class:: HttpResponseNotFound
Acts just like :class:`HttpResponse` but uses a 404 status code.
.. class:: HttpResponseForbidden
Acts just like :class:`HttpResponse` but uses a 403 status code.
.. class:: HttpResponseNotAllowed
Like :class:`HttpResponse`, but uses a 405 status code. Takes a single,
required argument: a list of permitted methods (e.g. ``['GET', 'POST']``).
.. class:: HttpResponseGone
Acts just like :class:`HttpResponse` but uses a 410 status code.
.. class:: HttpResponseServerError
Acts just like :class:`HttpResponse` but uses a 500 status code.
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